Communication devices such as User Equipments (UE) are also known as e.g. mobile terminals, wireless terminals and/or mobile stations. A user equipment is enabled to communicate wirelessly in a cellular communications network, wireless communications system, or radio communications system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
The user equipment may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, surf plate, just to mention some further examples. The user equipment in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another user equipment or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. By the base station serving a cell is meant that the radio coverage is provided such that one or many user equipments located in the geographical area where the radio coverage is provided may be served by the base station. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the user equipment within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Special Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
In the context of this disclosure, the expression downlink (DL) is used for the transmission path from the base station to the user equipment. The expression uplink (UL) is used for the transmission path in the opposite direction i.e. from the user equipment to the base station.
In cellular communications network as described above it is fundamental that it is supported that an active and connected user equipment when moving may switch from being served in one cell to instead be served in another cell. This may in general be referred to as mobility.
It is preferred that the switching from one serving cell to another does not negatively affect services provided to the user equipment in the cellular communications network, or at least that any degradation is not resulting in a negative user experience. Hence, it is in general desirable to facilitate cell switching. Today numerous different solutions and concepts exist for this. One such concept is Neighbour cell Relations (NR). In general, NR is about keeping track of relations to neighbour cells for a cell. A neighbour cell here refer to a cell that is so close that it may be expected that a moving user equipment will switch to the neighbour cell when moving. Typically this means that the neighbour cell has overlapping radio coverage with the cell of which it is neighbour. With NR associated with a source cell serving a user equipment, the source base station may have information available, which information may facilitate switching to a neighbour cell where the user equipment is suitably served next. Such neighbour cell may be referred to as target cell.
For cellular communication networks in general, but in particular for networks of today, such as LTE networks, with a great amount of neighbour cells, it is desirable not only to update the NR by adding new neighbour cell relations, but also to maintain and update the NR regarding already added cell relations, e.g. to change priority among existing cell relations and to remove cell relations.
Switching of a user equipment from being served in a source cell by a source base station to instead being served in a target cell by a target base station, may involve that the source base station communicates with and prepares the target base station about the switching. This may be referred to as prepared mobility, or handover, referring to handover of the user equipment by and from the source base station to the target base station. In case of prepared mobility, the target base station typically report back a successful switch to the source base station and NR may be updated accordingly.
However, switching of the user equipment from being served in the source cell to instead being served in the target cell may also be carried out without the above-described preparation of the target base station. This may be referred to as unprepared mobility. It is desirable to be able to update the NR in view of the result of the cell switching also in such cases. However, a successful switch is not to be identified until the switching is complete, when the user equipment is being served in the target cell. However, at this point in time and in the case of unprepared mobility, there is no reporting of the successful switch for updating the NR of the source cell.